Neil Armstrong and Buzz Aldrin

Ralph Morse / Time Life Pictures / Getty

The risks were otherworldly. If the engine designed to launch the men failed, they would crash. If the engine designed to lift them out of the moon's orbit failed, they would be forever lost in space. If the engine designed to return them to Earth failed, they would burn to death. There were solar and cosmic radiation to worry about, micrometeorites, lunar gravitational fields and whatever surprises the mysterious vacuum that is space might contain.

Eight years earlier  many moons ago  the space program had begun in earnest: Alan Shepard chased Gagarin, becoming the first American in space; John Glenn orbited, becoming the first American to do that; President John F. Kennedy made a new promise, that America would put a man on the lunar surface before decade's end; and the Mercury program yielded to Apollo. Twenty Apollo missions were launched between 1960 and '72, and much else had happened along the bumpy road to the moon: In January 1967, three U.S. astronauts perished in a fire while trapped in their command module during an on-ground launch simulation. Three months later, Russian cosmonaut Vladimir M. Komarov plunged to his death during reentry after his parachute lines tangled.

By the time veteran American astronauts Neil Alden Armstrong, Michael Collins and Edwin Eugene "Buzz" Aldrin Jr. were in preparation for their 1969 attempt at the moon, it appeared NASA had finally taken the lead over the Soviet Union in the race to conquer this next frontier. Apollo 11, 6.5 million pounds of space-age technology, lifted off on July 16, 1969, thrust toward space from Cape Kennedy, Fla. Three days later, Commander Armstrong, a former U.S. Navy pilot with a degree in aeronautical engineering; Aldrin, a former Air Force pilot with a Ph.D. from M.I.T. in aeronautics and astronautics; and Collins, a former Air Force pilot  each of them born in 1930  were hundreds of thousands of miles from home, circling the moon. The amazing drama was unfolding.

Armstrong and Aldrin climbed aboard the lunar module they had named the Eagle. Their compartment was nine feet high, 13 feet wide and 14 feet long and, besides its communication center, contained nothing more than the men, a guidance computer and some food and water. This wasn't really about scientific inquiry, this was about getting there: The Eagle had been designed for lunar landing, lunar liftoff and ultimate rendezvous with the command and service module, manned by Collins during his teammates' absence.

On Sunday, July 20, the lunar module broke from the CSM. "The Eagle has wings," Armstrong said as he and Aldrin started to make their way the 69 miles to the landing site. Suddenly, Armstrong saw below him a "football-field-sized crater with a large number of big boulders and rocks." He seized the manual controls and piloted the ship to safety, touching down on the intended target, the promisingly named Sea of Tranquility. After reporting the necessary technical information, Armstrong spoke the second of three phrases that still echo all these years later: "Houston, Tranquility base here, the Eagle has landed."

A world watched rapt as shadowy images, beamed back through space, seemed to show a man descending a short ladder and stepping onto the moon. What did he say? Did you hear what he said? What Armstrong said  "That's one small step for a man, one giant leap for mankind"  seemed perfect at the time, even if scientists, philosophers and the man in the street would debate in the years ahead how, precisely, getting to the moon represented a leap for mankind.

In any event, the Eagle's two-man crew went on to perform each of its duties on the lunar surface without surprise or malfunction. Toddling along in space suits built to withstand temperatures from minus 250i F to 250i above, as well as any micrometeorites that might be zipping about, Armstrong and Aldrin collected 50 pounds of rock and soil samples. They set up a seismometer to measure earthquakelike activity, a reflector to pick up moon-bound laser beams sent from Earth to measure the exact distance (turns out, 239,000 miles), and a sheet of foil to trap gases for study back at home. Armstrong and Aldrin spent two hours and 31 minutes walking on the moon before they clambered back into the Eagle, which lifted off serenely and rejoined the mother ship.

For the next three days, they and Collins cruised "right down U.S. 1," as Armstrong put it. "Very smooth, very quiet ride." On July 24, 1969, after crashing through Earth's atmosphere at some 25,000 miles an hour, generating temperatures nearing 4000i F, they splashed down in the Pacific, 15 miles from the recovery ship. They were entirely surrounded by a world in awe.

That wasn't the end of it, of course. The saga of Apollo 13, marooned in space before being dramatically reeled back to Earth, would follow in 1970. In 1972 the Apollo program would close up shop; the final tab would come to $20.4 billion. NASA's recyclable-craft shuttle program would be marked by a string of glorious successes  a cosmic fix-it operation for broken satellites, a taxi to the space stations  and the horrifying tragedy of the Challenger explosion in 1986. The Hubble telescope would probe deep space, and Pathfinder would find the surface of Mars. But all these years later, one space adventure still seems magical. Do you believe we put a man on the moon?